Fabrication of the seamless tubing with multi-layered metals provides superior corrosion, strength, or performance properties over that offered by tubing with only a one layer composition. The demand for high performance nuclear fuel cladding material is increasing due to higher nuclear fuel burn-ups and longer component lifetime requirements. Generally, the extrusion billet is assembled with multiple metallic cylinders of different alloys to produce a thin inside or outside layer. Typical products include a zirconium alloy outside layer on a zirconium alloy base material called duplex, a zirconium inside layer with a zirconium alloy base called barrier, or a zirconium layer between two zirconium alloy layers called triplex.
The process involves machining the zirconium or zirconium alloy components into base and liner assemblies. The components are typically cleaned to remove foreign debris like dirt and oil by pickling in baths of hydrofluoric and nitric acids before assembling into billet components. The annular opening at each end of the component is sealed by electron beam welding the end joints in vacuum. The welded billet is preheated between 550.degree.-750.degree. C. and extruded into a seamless tube. The extrusion cycle metallurgically bonds the dissimilar metals by temperature and pressure. The stringent quality requirements of the nuclear industry require inspection by ultrasonic techniques for bondline defects. The sensitivity of the ultrasonic test typically detects defects larger than 125 .mu.m in transverse width.
The metallurgical bond between the two metallic layers is influenced by the extrusion cycle and component cleaning process prior to billet assembly. The short extrusion cycle may not adequately bond the two or more metallic layers especially if contamination exists in the annulus of the billet. Thus, U.S. Pat. No. 4,977,034 proposed to heal the bondline defects by hot isostatic pressing instead of eliminating the cause of defects. The contamination is typically of a zirconium-fluoride species that remains chemically bonded to the cleaned component after the hydrofluoric acid pickling. During the extrusion cycle, regions of the bondzone with a high concentration of fluoride-rich residue form voids where the dissimilar metals fail to bond. Small bondline voids may not be detected with ultrasonic inspection but can be revealed by destructive testing. Bondline defects can be detrimental to the fuel cladding's performance since a large void can create discontinuities in the heat transfer efficiency and cause a localized increase in the corrosion rate for the duplex type tubing. The present invention provides a process to improve the bond integrity between the metallic layers by cleaning the cylindrical components by ice blasting.